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> Need help for diagnosis -- funny Lambda readings, ECU problem or Lambda sensor ?
billyleung_146
post 8th December 2017 18:15
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1.3 8v
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Attached Image


As shown in the photo, the car had been running for 15 mins and up to temperature, but the "Lambda sensor status" always stays at COLD. And the "Lambda sensor integrator" stays at 0.0.

Meanwhile, the "Lambda sensor signal" stays at around 450-480 mV. No matter what I do, for example, cracking open the throttle, staying at 3000 rpm or even disconnect a vacuum line, the Lambda signal only varies between 440-510 mV. It wouldn't go lower or higher....

It seems like a faulty Lambda sensor to me, right? But I did changed the Lambda sensor 10000 km ago. Although it was a cheap replacement one costed only 20 on ebay.

The last think I hope is that it is possibly the ECU's problem??


Thanks a lot!
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billyleung_146
post 8th December 2017 18:22
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More info to add:

1) 1997 146ti 2.0 alloy top engine with motronic M2.10.4 ECU

2) The car just failed the MOT for Lambda value too high (too lean, excess oxygen in the exhaust gas). And the plugs did suggest a lean condition.

3) I did check the wiring, the pins of the Lambda connector did connect to the correct pins of the ECU

4) I tried to unplug the Lambda sensor while the engine running and then measured the raw voltage of it. The voltage dropped gradually from 450mV to 0. This is what I don't understand.
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dante giacosa
post 8th December 2017 20:31
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Hey Billy-

I think you might have answered that yourself...

You can't skimp on the expense of the key sensors, I don't think. There are only two or three that you need to get the real thing.

The lambda is one of them I think- you can't expect much from a 20 sensor!

I'm rocking a 1.8 TS 146 myself (plastic top) and I just replaced the lambda this week.

Admittedly not without expense- the part number for me; if it's any use for you was 46750241, and I paid 78 + vat.

You don't want to wish for ECU problems!


Any chance of a picture of your car..?
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billyleung_146
post 9th December 2017 00:15
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QUOTE(dante giacosa @ 8th December 2017 20:31) *
Hey Billy-

I think you might have answered that yourself...

You can't skimp on the expense of the key sensors, I don't think. There are only two or three that you need to get the real thing.

The lambda is one of them I think- you can't expect much from a 20 sensor!

I'm rocking a 1.8 TS 146 myself (plastic top) and I just replaced the lambda this week.

Admittedly not without expense- the part number for me; if it's any use for you was 46750241, and I paid 78 + vat.

You don't want to wish for ECU problems!
Any chance of a picture of your car..?


Thanks for the reply. Let me look for a photo later.

I am still wondering what the "Lambda sensor integrator" reading represent. Is it indicating the short period fuel trim? If so, what is the unit? After reviving the engine for a while, the "integrator" value eventually didn't stay always at zero, but went negative.

The graph captured while idling:
Attached Image


The graph captured while holding rpm at 2500-3000 (see the 2 plateau in the air flow curve) :
Attached Image
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dante giacosa
post 9th December 2017 09:14
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sorry-

I can't bring much to that...
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